The present invention is directed to a treating composition, treated glass fibers and process for producing an improved dispersion of glass fibers in aqueous solution.
More particularly, the present invention is directed to treated glass fibers having improved dispersibility in aqueous solutions, sizing composition for treating glass fibers, and process for producing an improved dispersion of glass fibers in aqueous solution, and a more uniform, sheet-like, glass fiber product.
Glass fibers have been used in combination with other types of fibers or alone in the production of paper-like sheet materials. Glass fibers have been used as a supplemental fiber in specialty synthetic fiberwood pulp composite papers. It has also been recognized that small diameter glass fibers can be used to produce paper-like sheet material that has a high strength and can be used as air or liquid filtration papers. With the growing concern of possible health hazards associated with asbestos fibers, the use of glass fibers as a replacement for asbestos fibers in producing sheet-like material is being investigated.
The glass fibers differ from natural cellulose fibers or asbestos fibers in that the glass fibers are more difficult to disperse in water and they do not fibrillate in the usual paper-making sense. The dispersion problem occurs when a slush, an aqueous suspension of dispersed fibers, of the glass fibers or the combination of glass fibers and cellulose fibers is prepared as a preliminary step to the formation of a wet web. The dispersion problem of glass fibers is caused by several factors including the length of the fibers, the electrical charges on the fibers, the diameter of the fibers, the differing water absorbtion characteristics, and the presence of textile sizes or finishes on the glass fibers. When the glass fibers have a small diameter, i.e., a micro fiber with a diameter up to around 6.4 microns, the glass fibers produced without a sizing composition, or with a sizing composition that can be easily removed, or with a sizing composition containing a water-dispersible starch binder have found some utility. When the diameter of the glass fibers increases above the micro size, the problem of poor dispersibility becomes increasingly significant.
The art in trying to improve the dispersibility of glass fibers has employed the use of additional chemicals that may be anionic, cationic or nonionic depending upon the nature of the fiber and may be supplied as a finish on the fiber or added separately to the aqueous system. For example, the art discovered that an acid pH obtained by the addition of strong mineral acids or sodium hexametaphosphate was useful in dispersing glass fibers (U.S. Pat. No. 3,749,638 and U.S. Pat. No. 2,919,221). Also the art has shown that polyacids, like phosphoric, and carboxy methyl cellulose, can be used as dispersing aids (U.S. Pat. No. 2,802,734). In addition, the art has shown that linear polysiloxanes containing at least 6 silicon atoms with each atom having 2 non-hydrolyzable olephilic groups can be used to disperse glass fibers (U.S. Pat. No. 4,052,256). The use of these additional chemical agents may be useful in dispersing micro size glass fibers. There is a need in the art for a sizing composition for glass fibers that renders the protection needed for glass fibers against further processing while at the same time does not interfere with but actually assists in dispersing glass fibers in an aqueous solution. Also, there is a need in the art for glass fibers in any form and in diameters larger than micro-diameters that have better dispersibility in aqueous solutions to form a more uniform sheet-like, glass fiber product.
It is an object of the present invention to provide a sizing composition for glass fibers that yields sized glass fibers with improved dispersibility in aqueous solutions.